If $x \diamond y = x-3y$ and $x \veebar y = 3x-4y$, find $(6 \diamond 3) \veebar 3$.
Solution: First, find $6 \diamond 3$ $ 6 \diamond 3 = 6-(3)(3)$ $ \hphantom{6 \diamond 3} = -3$ Now, find $-3 \veebar 3$ $ -3 \veebar 3 = (3)(-3)-(4)(3)$ $ \hphantom{-3 \veebar 3} = -21$.